Information flow in the brain is mediated by transduction of electrical information into chemical information and back again at chemical synapses. Synapses are made up of crucial cellular machineries that orchestrate a balance of membrane traffic to and from the plasma membrane. Our goal is to develop detailed quantitative understanding of the synapse both in terms of physiological responses to action potential stimuli as well as the molecular underpinnings of its function. We recently developed sensitive approaches that allow us to determine the detailed kinetics of endocytosis as well as the relative size of recycling and resting vesicle pools. These methods allow us to perform functional tests of how specific proteins are controlling various aspects of presynaptic function. The goal of this project has 2 main AIMS. Our first AIM will extend our recent findings that the recycling and resting vesicle pool fractions in nerve terminals is controlled by the balance of two enzymatic activities, the phosphatase Calcineurin and the kinase CDK5. Our goal is to specifically test the hypothesis that the abundant presynaptic phosphoproteins Synapsin and -catenin which are substrates of CDK5 are critical to mediating this control of these vesicle pools. We will also determine which cyclin controls CDK5.The second AIM will explore a fundamental property of nerve terminals, the retrieval of synaptic vesicle components. We will test the hypothesis that during vesicle recycling the different SV membrane proteins remain together, by simultaneously observing the endocytic behavior of different SV proteins. We will examine the importance of the known change in phosphorylation state (driven by CDK5) that dynamins, amphiphysin and synaptojanin undergo with activity by examining endocytosis properties at nerve terminals in which these proteins have been fully replaced by phosphomimetic mutants. Finally in our recent work we discovered that even in the absence of major brain dynamins 1 & 3 endocytosis persists. This result is enormously surprising and we are compelled to understand how endocytosis can be achieved in the absence of these once-thought critical mechanoenzymes. We will test hypotheses that the endocytosis that persists in the absence of the major brain dynamins, Dynamin 1 and 3 is driven by either the remaining dynamin (Dynamin 2) or one of two known BAR domain proteins, Amphiphysin or Syndapin.